Rotary tuner with temperature compensating means in operating arm



July 26, 1960 H T. LYMAN ROTARY TUNER WITR TEMPERATURE COMPENSATING MEANS IN OPERATING ARM Filed Oct. 29, 1958 50 3g 20 48 I 2,e 72 24 A L44 lo g a, ,8 I& 45

J Ha 141 7; 31

ra [7? FIG, 5 7

fliornays United States Pateht O ROTARY TUNER WITH TEMPERATURE COM- PENSATING MEANS IN OPERATING ARM Harold T. Lyman, Milford, Conn., assignonto Aladdin Industries, Incorporated, Nashville, Tenn., 21 corporation of Illinois Filed Oct. 29, 1958, Ser. No. 770,473

4 Claims. (Cl. 25040) This invention relates to a new and improved tuner adapted to cover a wide range at high radio frequencies. One object of the present invention is to provide a new and improved wide range tuner having a toroidal coil,

together with a rotary tuning element for varying the effective inductance of the coil.

I A further object is to provide a new and improved tuner of the foregoing character in which the entire tuning range is covered by rotating the tuning element through some what less than one revolution.

Another object is to provide a new and improved tuner of the foregoing character which is so arranged as to avoid the necessity for sliding electrical contacts.

A furtherobject is to provide a new and improved rotary tuner which is arranged so as to minimize the effect of temperature changes upon the operating frequency of the tuner. I

Still another object is to provide a tuner of the foregoing character which is extremely compact, yet easy to manufacture and low in cost.

Further objects and advantages of the present invention will appear from the following description, taken with the accompanying drawings in which:

Figs. 1 and 2 are front and side elevational views of a rotary tuner to be described as an illustrative'embodimerit of the present invention.

Fig. 3 is a fragmentary enlarged sectional view, taken generally along a line 3-3 in Fig. 1.

i As already indicated, the drawings illustrate a rotary tuner utilizing a toroidal coil 12. It will be seen that "the coil 12 is provided with a ring-shaped insulating form or support 14, which may be made of various plastics, ceramics or the like. The coil 12 comprises a flat, ribbonlike conductor 16 which is coiled around the form 14 in a generally helical fashion. As shown, the width of the ribbon conductor 16 and the pitch of the turns may vary along the length of the coil, so as to obtain a desired or suitable variation of inductance per unit length. While the ribbon conductor 16 may be wound or otherwise end surfaces 22 and 24. Rounded corners 26 are provided between the surfaces 1824. The width of the surfaces 18 audit) is substantially greater than that of the surfaces 22 and 24, with the result that the coil 12 has an elongated, oblong, cross section.

To vary the efiective inductance of the coil 12, the

"m mo is provided with a rotary tuning element 28, adap ed to be operated by rotating a shaft 30. It will be seen that the shaft 30 extends along the axis of the toroidal coil 12. The illustrated tuning element 28 com- Patented July 26, 1960 prises inner and outer arcuate segments or electrodes 31 and 32 which are cylindricallycurved and are adjacent the inner and outer sides of the toroidal coil'12.' The electrodes 31 and 32 are preferably madeofmetal so as to be electrically conductive. .In this case, the inner seg ment 31 is connected to the shaft 30 by means of an arm 34 which may be formed integrally with the segment 31, or may be suitably secured thereto. The inner end of the arm 34 is rigidly secured to a collar 36 which is mounted on the shaft 30. A set screw 38 or the. like may be employed to secure the collar 36 to'the shaft 30. It is preferred that the collar 36 and the shaft 30 be'made' of metal sons to be electrically conductive.

As shown, the outer segment 32 is'connected to the arm 34 by means of an extension plate 40 which is secured to the arm 34 by screws '42 or other suitable means. The illustrated screws 42 extend through the plat'e'40 and are tapped into the arm 34. The segment 32 may be staked, welded, or otherwise rigidly secured to the extension plate 40.

-It will be seen that the inner'and outer electrodes 31 and 32 are concentric with the shaft 30, while the arm 34 and the extension plate 40 are disposed in planes perpendicular to the shaft. The electrodes 31 and 32 are connected together at one end by the plate 40. It is preferred to connect the other ends of the electrodes 31 and 32 together by means of a conductive member 44, shown in the form of a generally channel-shaped clip adapted to fit over the ends of the electrodes. While the clip 44 may simply be retained by friction on the electrodes 31 and 32, it is preferred to form soldered joints 46 and 48 between the clip and the electrodes 31 and 32.

It Will be understood that the electrodes 31 and 32 are in energy exchange relation with the coil 12. It is preferred to provide insulation or dielectric material 50' between the coil and the electrodes, so that the energy exchange will be of a capacitive character. While the insulation may be provided simply by air gaps between the coil and the electrodes, it is preferred that the insulation 50 take the form of an insulating coating applied to the coil 12. It will be understood that the coating could be applied to the electrodes 31 and 32. However, when applied to the coil, the coating 50 provides not only insulation around the coil, but also protection against mechanical abrasion or damage. It is desirable to provide slight clearance between the coating 50 and the electrodes 31 and 32, so that the electrodes will move freely along the coil 12. The clearance is clearly indicated in Fig. 3, and, in fact, is somewhat exaggerated for clarity of illustration. The thickness of the coating 50 is also exaggerated. Actually, the thickness of the coating plus the clearancemay amount to only a few thousandths of an inch.

The illustrated tuner is of the two-terminal type. One end of the coil 12 and the interconnected electrodes 31 and 32 constitute the two terminals of the tuner. Thus, a lead 54 is shown connected to one end of the coil 12 to 7 form a circuit connection thereto. While a circuit connection could be made to the electrodes 31 and 32 by means of a sliding contact, it is preferred to provide a capacitive connection so as to avoid the electrical noises that often develop from the use of sliding contacts. Thus, the illustrated tuner is provided with a stationary ring or collar 56 which is mounted around the shaft'30 and is insulated therefrom by means of a thin insulating film or coating 58, the shaft being freely rotatable within the ring 56. The film or coating 58 may be applied to the inside of the ring 56, and a sliding fit may be" provided between the coating and the shaft. In the illustrated arrangement, the shaft '30 is c'onductivel'y "connected to the electrodes 31 and 32, while the wages is capacitively coupled to the shaft. A lead 60 maybe attached to the ring 56 to provide for a circuit connection to the electrodes. The insulating film 58 may be made extremely thin so as to afford maximum capacity between the ring and the shaft.

It will be understood that the interconnected electrodes 5 31 and 32 are capacitively coupled to the portion of the coil 12 opposite the electrodes. Only the portion of the coil 21 between the end lead 54 and the electrodes 31 and 32 is efiec'tively connected into the circuit between the leads 54 and 60. Any movement of the electrodes 31 10 the coil. Moreover, the sleeve tends to act as a shortcircuited turn, inductively coupled to the portion of the 20 coil within and adjacent the sleeve. In this way the sleeve tends to damp out or suppress undesired resonances in the portion of the coil within the'sleeve, and in the unused portion of the coil adjacent the sleeve.

In order to minimize the effect of temperature variations upon the tuner, it is preferred that the coil form 14 be made of a material having a co-efiicient of thermal expansion corresponding to that of the metal employed in the electrodes 31 and 32. With this arrangement any dimensional variation in the electrodes, due to temperature changes, will be matched with corresponding dimensional variations in the coil 12.

Temperature variations will tend to change the clearances between the coil 12 and the electrodes 31 and 32. Any variation in the clearances will tend to change the capacitance between the coil 12 and the electrodes 31 and 32. In order that the net change in capacitance may be zero or nearly so, it is preferred that the extension plate 49 and the clip 44 be made of a material having a substantially greater coefiicient of thermal expansion than the arm 34. The difference in the co-efiicients of expansion is made such that any change in the clearance between the electrode 31 and the coil 12 will be compensated by an opposite change in the clearance between the electrode 32 and the coil.

As already indicated, the coil form 14 is preferably made of ceramic or plastic material, while the arm 34- is made of metal. With this arrangement, the arm 34 will. normally have a co-efficient of expansion somewhat greater than that of the coil form 14. temperature, the arm as will thus expand more than the coil 12, with the result that the clearance between the electrode 31 and the coil will be decreased. This decrease in clearance causes an increase in the capacitance be-, tween the electrode 31 and the coil 12. It will be understood that the coil 12 is resonated by its own inherent distributed capacitance, plus the capacitance of the circuit connected between the leads 54 and 60. Normally, the circuit capacitance is much greater than the distributed capacitance, and thus is a much more important factor in resonating the coil 12. The capacitance between the coil and the electrodes 31 and 32 is in series with the circuit capacitance, and thus is also a factor in the resonating of the coil. A thermal variation in the capacitance bu tween the coil and the electrodes will tend to change the resonant frequency of the tuner.

Normally, the capacitance between the coil and the electrodes 31 and 32 is substantially greater than the circuit capacitance connected between the leads 54 and 60. For example, a typical value of circuit capacitance might be twenty micro-microfarads, while the capacitance between the coil and the electrodes may amount to about sixty micro-microfaradsf With this relationship, the net change in the resonating capacitance is only .a fraction 75 With increasing 50 4 of any variation of the capacitance between the coil and the electrodes.

The tendency of the clearance between the electrode 31 and the coil 12 to decrease with increasing tempera= ture is compensated for by making the plate and the clip 44 of a material having a substantially higher coeflicient of expansion than the arm 34. With this arrangement, the clearance between the electrode 32 and the coil increases with increasing temperature. Moreover, the rate of increase is greater than the rate at which the clearance between the electrode 31 and the coil 12 decreases. Thus, the increase in the capacitance between the electrode 31 and the coil 12 may be nullified by the decrease in capacitance between the electrode 32 and the 5 coil. In this way, the net variation in the'capacitance ctween the coil 12 and the interconnected electrodes 31 and 32 may be made Zero or nearly so. Thus, a minimum of thermal drift in the resonant frequency will be experienced as the tuner is warmed up to its normal operating temperature by the heat generated in the associated electronic equipment.

It will be apparent that the tuner provides a smooth variation in its resonant frequency over a wide range. All sliding contacts are avoided, so that electrical contact noise is eliminated. Moreover, thermal drift of the tuner is minimized.

With all of these advantages, the tuner is extremely compact, easy to manufacture'and low in cost. In the drawings, the tuner is shown on a fairly large scale for clarity of illustration. However, the tuner may actually be only a fraction of the illustrated size, particularly when the tuner is to operate at high radio'frequencies, such as those employed for television and similarservices. Several of the tuners may easily be ganged together, sim- 0 ply by connecting the individual shafts of the tuners together, or providing a common shaft.

Various modifications, alternative constructions, and equivalents may be employed without departing from the true spirit and scope of theinvention as exemplified in the foregoing description and defined in the following claims. a

I claim:

1. In a radio frequency tuner, the combination com- .prising a toroidal coil including a fiat ribbon-like con- 5 ductor coiled around a ring-shaped insulating form, said coil being generally rectangular in cross section, inner and outer segmental electrodes movable along said coil in closely adjacent energy exchange relation thereto on the inside and outside of said ring-shaped form, a dielectric film around said coil to provide for capacitive energy exchange between said coil and said electrodes, a .conductive rotatable operating shaft extending along the axis of said ring-shaped form, a conductive metallic arm forming a rigid connection between said inner electrode and said shaft, a first metallic member forming a rigid connection between said second electrode and said arm, a second metallic member connected between said electrodes at the ends thereof opposite from said arm, and a conductive ring received around said shaft with dielectric material therebetween, said ring being capacitively coupled to said shaft and constituting one terminal of said tuner, one end of said coil constituting the other terminal of said tuner, said arm having a greater co-etiicient of thermal expansion than said insulating form, each of said 5 metallic members having a substantially greater cotric material'between said coil and said electrodes to provide for capacitive energy exchange therebetween, a control shaft extending along the axis of said coil, an arm forming a rigid connection between said shaft and one end of said inner electrode, a first member forming a rigid connection between said arm and one end of said outer electrode, a second member connected between the opposite ends of said inner and outer electrodes, said electrodes constituting another terminal of said tuner, each of said members having a co-efficient of thermal expansion which is substantially greater than that of said arm to compensate for differential expansion between said arm and said insulating form.

3. In a radio frequency tuner, the combination comprising a toroidal coil including a conductor coiled around a ring-shaped insulating form, inner and outer conductive electrodes movable along the inside and the outside of said coil in closely adjacent relation thereto with dielectric material between said coil and said electrodes to provide for capacitive energy exchange therebet-ween, a control shaft extending along the axis of said coil, an arm forming a rigid connection between said shaft and one end of said inner electrode, a conductive member forming a rigid connection between said arm and one end of said outer electrode, said electrodes constituting another terminal of said tuner, said member having a co-efficient of thermal expansion which is substantially greater than that of said arm to compensate for differential expansion between said arm and said insulating form.

4. In a radio frequency tuner, the combination comprising a toroidal coil including a conductor coiled around a ring-shaped insulating form, inner and outer conductive electrodes movable along the inside and the outside of said coil in closely adjacent relation thereto with dielectric material between said coil and said electrodes to provide for capacitive energy exchange therebetween, a control shaft extending along the axis of said coil, an arm forming a rigid connection between said shaft and one end of said inner electrode, a conductive member forming a rigid connection between said arm at one end of said outer electrode, said electrodes constituting another terminal of said tuner, said member having a co-efiicient of thermal expansion which is substantially different from that of said arm to compensate for differential expansion between said arm and said insulating form.

References Cited in the file of this patent UNITED STATES PATENTS 1,913,978 Ewen June 13, 1933 2,009,013 Karplus July 23, 1935 2,558,487 Hills June 26, 1951 2,873,373 Lyman Feb. 10, 1959 FOREIGN PATENTS 335,309 Germany Mar. 30, 1921 

